This disclosure relates to a drive for split sickle bars on harvester headers, such as combines, swathers, mower-conditioners and similar crop and hay cutters, where the cutter bar and sickle are long, so two sickle bar sections are reciprocated in opposite directions, and operated with separate reciprocating drives. The sickle bar sections move in opposite directions as they are separately stroked, and the present disclosure teaches synchronizing the drives so that the sickle bar sections will not go out “of time” and cause objectionable vibration.
Large harvesters and combines for harvesting grain have headers that are up to at least 36 feet long, and it is common practice to have a split sickle bar, that is, two sickle bar sections driven from the opposite ends of the header and the moving linearly in opposite directions. It is also well known to use a “wobble” drive that converts a rotary motion into a linear motion for driving the sickle bar sections. It is important that the sickle bar sections remain in time, that is, so that they complete their stroke in each direction at the same time. This minimizes vibrations and insures clean cutting of the grain stalks in the center of the header.
It is also desirable to have hydraulic motor drives for providing the rotary motion to the wobble drives. At the present time, the hydraulic motors used are generally, but not necessarily series connected. However, due to the normal internal leakage of the motors, the second motor in the series connection (the slave motor) will rotate at different rpm from the first or master motor. Small differentials in speed will cause the sickle bar sections to go in and out of “timing” or synchronization and strip the crop, rather than cut it, and also cause vibration.
At present, most split sickle bars cannot be kept in perfect synchronization, unless there are non-slip drive connections to the sickles (which are costly and have other drawbacks), so to create a non-perceptible vibration the two sickle bar sections are intentionally driven at sufficiently different speeds (for example at a 25 rpm difference) so the “beat” frequency is rapid and not highly objectionable, for example every 2 or 3 seconds. This does cause vibrations of the machines, but it is tolerated by the operators. The overlapping center sections of the two sickle bar sections will be in a position where the crop is torn or stripped, rather than cut, for short intervals of time, so while the cutting in not ideal, the tearing of the crops is intermittent, rather that for long periods of time.
The inner ends of the sickle bar sections overlap in the center of the header during their strokes, for complete cutting, and if they go out of time, the overlap length in the middle of a header will go from ideal cutting to stripping and pulling the crop being harvested. Also the mechanical imbalance of the weight and the inertia of the sickle bar sections will go from “balanced” (in sync) to totally out of balance, which is essentially with the two sections running like one long sickle bar insofar as vibrations are concerned. The vibrations can be felt by the operator, and the vibrations also reduce the life of the machine.
Attempts have been made to solve the synchronization problem. For example, U.S. Pat. No. 5,787,786 shows a dual hydraulic oscillator for a reciprocating cutter that provides for synchronizing the outputs to a split sickle bar section drive.